The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. In addition to IC components becoming smaller and more complex, wafers on which the ICs are fabricated are becoming larger. For example, current wafer size is 300 mm, and in coming 5 year may enter into 450 mm wafer production.
Wafers are processed in many ways, some of which are done while the wafer is secured on a planar wafer platform (e.g., table, holder, or chuck) in a process chamber of a wafer processing tool. In many steps of wafer processing, such as pre-cleaning, post-cleaning, or various etching steps, chemical materials such as cleaning agents or etchants are added to a surface of the wafer to form or modify layer(s) of material on the surface. To boost chemical reactions for the process, the wafer often needs to be heated to a suitable temperature. In the conventional methods practiced in the current art, the heat is directly supplied to the layer formed on the wafer by an overhead heater located above the wafer, and thereby, to the wafer below. Some heaters are configured to move over the wafer surface, and some are fixed.
The current methods practiced in the art, however, have a several deficiencies. One is caused by a non-uniform heat distribution across the wafer. Since the overhead heater heats the chemical layer only locally, the layer and the wafer below cannot have uniformity in temperature. Even if the heater is configured to move around over the wafer while heating, the uniformity obtainable is limited and the non-uniformity cannot be totally eliminated. The non-uniformity in temperature is aggravated by the increased wafer size, as well as any non-uniformity in the chemical layer itself caused by the currently used system of depositing chemical material on the wafer, which typically uses sprayers. With such sprayers, whether moving or fixed, the material sprayed on the wafer will not be uniform.
Another deficiency is due to directly heating up the chemical materials. The temperature to which the chemical materials are heated is subject to a temperature constraint imposed by the chemical property of the chemical materials. For example, the chemical material may need to be heated up past its boiling point for various reasons, at which the material changes from liquid to gas. Since the temperature of the chemicals does not change for the duration of the phase change of the chemicals despite continued application of heat energy, the temperature of the wafer does not increase as desired at the cost of heat energy during this period. Moreover, the abrupt, dramatic volume expansion of the chemical gas following the liquid-gas phase change not only impairs the reaction rate from the loss of available liquid state chemicals at which most chemical reactions most actively occur, but also causes pattern damage or collapse. Further, in the high temperature environment in the vaporized phase of the chemicals in which the temperature rapidly increases, it is much harder to control or fine-tune a temperature profile on the wafer as precisely as desired for optimum reaction rate and uniformity.
Therefore, to prevent the pattern collapse induced by sudden volume expansion of vaporized chemical gas, to ensure more fine-tuned control over the temperature of the wafer and thus over optimum reaction rate, and to obtain more temperature uniformity across the wafer, it is desirable to provide a method and a system for heating up a wafer that can produce a uniform, or any desired temperature profile on the wafer determined for optimum reaction rate. Further, it is also desirable to provide a method and a system for heating up a wafer that can provide a closer and finer control over the temperature of the wafer in a milder temperature environment that does not invoke the damaging expansion of the chemical gas on the wafer surface from its phase change.